Gravitational waves from black holes detected

Gwynston

Big announcment today:
Gravitational waves from black holes detected

Anonymo

Gwynston wrote: »

Big announcment today:
Gravitational waves from black holes detected

Big is an understatement. This is huge. Their main paper is here What's they've seen is two black holes of mass 29 times and 36 times the mass of our sun coalescing. During this coalescence the two black holes rotate each other (allowing us to infer their individual masses) before combining and in the process giving out some excess energy. They find that the mass of the combined black hole is 62 times the mass of our sun, and 3 solar masses have been ejected as gravitational radiation.

The effect of this gravitational radiation (or ripples in the fabric of spacetime) is to compress spacetime in one direction and stretch it in the other -- a kind of shearing.

How have they detected this? In two detectors (one on the east coast of the US, the other on the west coast) they've built (they being the LIGO team) observers. These are L-shaped so that on one leg of the observer you see the compression and on the other the stretching. They've put mirrors at the end of 4km tubes along each direction and a laser is sent in and split to go along each tube. If there are no gravitational waves then the two beams will travel the same distance and the light waves sent by the beam will bounce off the mirrors and combine back at the crux of the arms of the L and cancel each other out. If there's a gravitational wave the beams will have travelled different distances and will no longer cancel. A detector is put in place to measure this.

Why haven't we seen them before now? Even though the collision of two blackholes is amazingly violent (the energy of the ejected gravitational waves in the event seen has a power about 50 times that of all the stars and galaxies we observe!) it is pretty weak by the time it reaches us (from 1.3 billion light years away, or for those who prefer redshift it's at z=0.1). The sensitivity of the detector had to be that of the width of the human hair.

Why should we believe it? Because the two detectors saw the same thing at practically the same time (separated by 0.007seconds). They saw the same pattern, predicted the same masses for the separate black holes and for the coalesced black hole. The estimates for the signal to be a false alarm are at the rate of less than 1 per 203000 years. This is real!

Should we be excited by this? Well you can probably tell that I am! Up until now we had to use electromagnetic radiation (our eyes -- via telescopes, or infrared or ultraviolet) to see the universe around us. This radiation is NOT electromagnetic. We can now see the Universe in a totally different way, and probe things (like black holes) that we couldn't otherwise do directly. This has the potential for probing higher energy scales and maybe allowing us to find whether string theory is true, or, if not, allowing us to get much closer to the holy grail of the 'theory of everything'. This is a game changer!

Anonymo

Nice image of what's going on during the merger was in one of the papers so thought I'd add it

_Tombstone_

This new astronomy has crap pics.


Next step for this stuff is the Pathfinder.

http://touch.boards.ie/thread/2057531299/1/#post98549728

rolion

Sorry to all...but I don't get the "noise" around this event !
Anyone can help,please !??

gizmo555

rolion wrote: »

Sorry to all...but I don't get the "noise" around this event !
Anyone can help,please !??

Some good video explanations here:

The significance is firstly, it proves something about the nature of the universe first theorised by Einstein 100 years ago and much more importantly, it gives us a completely new way of observing the universe. As a scientist says in the 3rd of these videos, this is as significant as Galileo's first use of the telescope.

https://www.youtube.com/watch?v=Lcxt097G4Ps

https://www.youtube.com/watch?v=X30f_3gki48

https://www.youtube.com/watch?v=B4XzLDM3Py8

Anonymo

gizmo555 wrote: »

Some good video explanations here:

The significance is firstly, it proves something about the nature of the universe first theorised by Einstein 100 years ago and much more importantly, it gives us a completely new way of observing the universe. As a scientist says in the 3rd of these videos, this is as significant as Galileo's first use of the telescope.

https://www.youtube.com/watch?v=Lcxt097G4Ps

https://www.youtube.com/watch?v=X30f_3gki48

https://www.youtube.com/watch?v=B4XzLDM3Py8

The second video is excellent. It's produced by a guy who worked on gravitational waves for a number of years (and is a friend of mine!)

_Tombstone_

20 years after Einstein proposed them, he relooked at the math and thought he was wrong and they didn't exist.

http://astronomy.com/news/2016/02/even-einstein-had-his-doubts-about-gravitational-waves

The relook paper wasn't published cuz of errors and Einstein was raged they peer reviewed it - first time to experience it - and never submitted another to them.

He submitted it elsewhere where they to showed him errors.

dlouth15

India and China to start gravitational wave projects:

http://www.thehindu.com/sci-tech/science/indian-gravitational-wave-observatory-gets-union-cabinet-approval/article8248745.ece

http://phys.org/news/2016-02-gravitational-unveiled-china.html

figges

Anonymo wrote: »

The second video is excellent. It's produced by a guy who worked on gravitational waves for a number of years (and is a friend of mine!)

Yes excellent representation, fairly mind bending stuff. So does that mean if mass displaces space in space-time then time must move as well ??? The fact that gravity isn't the Newtonian force we non physicists believed it was is kind of disturbing tbh.

_Tombstone_

https://www.youtube.com/watch?v=ajZojAwfEbs

Anonymo

figges wrote: »

Yes excellent representation, fairly mind bending stuff. So does that mean if mass displaces space in space-time then time must move as well ??? The fact that gravity isn't the Newtonian force we non physicists believed it was is kind of disturbing tbh.

The equations of general relativity say that the space-time will be affected in a dynamical way by the presence of matter, but the equations (being non-linear) also say that the dynamics of space-time have an effect on the evolution of matter.

A nice way to think about relativity is to think about the core principle behind it which says (roughly) all non-accelerating observer in the same space-time experience the same physics. So picture that you're in an elevator (with no windows). As we are being accelerated towards the earth at around 10 metres per second per second this principle says that we cannot tell the difference between whether we are on earth moving up at the same acceleration (cancelling out the gravitational acceleration) or whether we are out in space and experiencing no acceleration at all - of course this ignores oxygen deprivation issues!

How does this relate to your question? We know light moves in straight lines if there is no mass to disturb it. If we are in an elevator accelerating up on earth and cancelling the earths pull, we should see the same straight light path as the guy in the weightless elevator out in space. This says that another guy standing on the surface of the earth must then see the light-ray being curved down, i.e. the presence of the earth must be curving the space-time.

This all sounds like bending of space - where does time come into it? Well we know light moves at a certain speed and all observers no matter how fast they are moving should measure the same speed. To satisfy this the usual addition of velocities (e.g. if I'm running at 10 mph forward on a train moving at 50mph you might say that compared to someone standing still near the tracks that I'm moving at 60mph) has to be altered so that now if I'm running at 10mph on a train moving at the speed of light the person standing near the tracks says that I'm moving at the speed of light! For this to work time slows down as you move faster. This also carries true to massive objects which cause a time dilation (slowing down). This is important for things like GPS to work, and this time dilation (which causes things like the twin paradox) has been found to be true experimentally - by comparing the time elapsed on clocks on space missions to those on earth, for example. But apply the core principle I spoke about earlier and we then find that the presence of mass must also effect how fast clocks run in this way. If you took a holiday for a week near a black hole when you returned you'd find everyone you knew had left this mortal coil centuries ago!

Is it disturbing? No! Newtonian physics is a perfectly good theory up to certain speeds and masses. Our day-to-day experiences deal with Newtonian physics which is why we find general relativity and quantum mechanics difficult to grasp. Then again if you were an insect living on the surface of a lake, you would think surface tension is far more important that gravitation and would find Newtonian gravity difficult to grasp!

figges

Thanks for the comprehensive reply.

From a passing interest in a scientific discovery leading to teetering into this thread I now have a more considered understanding of what gravity is and its universal significance. Previously it was just a vague notion.

Thanks to those who contributed, makes for something a bit special when you stumble upon something as interesting as this.

I do concede that for a relative lay person some of these concepts aren't easy to grasp.

When threads lead you to statements like Minkowskis, that state, somewhat dramatically ..

"Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality".

it does take more than a little absorbing.

Regardless of having studied quantum mechanics in chemistry, and having some appreciation of the uncertainty that exists at nano level it is never the less enlightening to get an insight into the uncertainty that exists at macro level, and the discoveries that are slowly releasing its secrets.

However in defence of the relative lay person, and my biology maybe a little shaky here, I would suggest that if one were an insect pondering surface tension and considering the merits of Newtonian physics they would likely either be in, “A Bugs Life” or instigating a revisionist approach to Darwinism.

Excellent thread.

It will be interesting to see what the astronomical world post the discovery of gravitational waves has to offer.

_Tombstone_

Another wave detected

http://www.sciencemag.org/news/2016/06/ligo-detects-another-black-hole-crash

JupiterKid

This is truly epoch making. And this is with ground based LIGO. Imagine what could be detected with a fully operational LISA system in space?

We have truly opened up a new field of astronomy. No doubt LIGO scientists are in line for a Nobel in the bit too distant future.

Anonymo

Almost as exciting as this, was the announcement a couple of weeks ago that the LISA pathfinder (this was a probe mission to assess the feasibility of LISA) was found to perform far above requirements The accuracy levels attained are astonishing. It's now fully expected that LISA will go ahead as planned for a launch in 2034

Capt'n Midnight

Good news everyone !

http://www.bbc.com/news/science-environment-40346410

The European Space Agency has just given the green light to the LISA mission to detect gravitational waves.

This will see lasers bounced between three identical satellites separated by 2.5 million km.

...
The earmarked launch date for LISA is 2034. Efforts will be made, though, to bring this forward because of the excitement that currently surrounds gravitational wave science.